The present invention relates to image upscaling.
Digital video is typically represented as a series of images or frames, each of which contains an array of pixels. Each pixel includes information, such as intensity and/or color information. In many cases, each pixel is represented as a set of three colors, each of which is defined by eight bit color values.
Pixel information within a frame may be missing such as boundary conditions that may result when executing a video conversion process, such as the conversion between interlaced television field signals and progressive frame signals. In other cases, a frame may be at a first resolution, such as standard definition, which is desirable to convert to a second resolution, such as high definition.
Standard techniques for pixel interpolation are based on application of classical linear filters. However, such techniques introduce various visual artifacts such as blurring of sharp edge patterns and detailed texture patterns in the image, ringing along edge contours, as well jaggedness along edge contours. Such artifacts generally cannot be avoided when standard linear filtering techniques are used for interpolation. Therefore, there is a need for improved techniques for pixel interpolation, such as techniques that are adaptive to local image patterns.
An improved technique for pixel interpolation is generally referred to as an edge-directed interpolation which seeks to generate a value for a missing pixel by extending the patterns in selected directions, expressed as edges which exist in the surrounding pixels of an image frame.
Unfortunately, it is difficult to determine the existence of an edge in an image and the direction of such an edge in an image. Erroneous estimates of the direction can lead to new visual artifacts in the image after interpolation. Therefore, there is a need for a robust technique for estimating the direction of a local edge pattern in an image. Furthermore, there is need for a robust image upscaling technique that considers the possibility of erroneous estimates of the direction, to avoid any visual artifacts. Furthermore, there is a need for an image upscaling technique with low computational complexity that can outperform standard linear filtering techniques in terms of visual quality.
In some images there tend to be a lot of texture, or regions where there are not well defined edges. In such a case, edge centric techniques have a tendency to identify false edges resulting in visual artifacts. Accordingly, it is desirable that a pixel interpolation technique is also suitable for texture based regions of an image.
The foregoing and other objectives, features, and advantages of the invention will be more readily understood upon consideration of the following detailed description of the invention, taken in conjunction with the accompanying drawings.